Beyond simply a list of 12 highly controversial calls, each of the above games has something in common: at the end of each contest, a referee or umpire needed to make a judgment call or decision. And on each of those calls, the referees favored the home team.

Take the Monday Night Football contest between the Patriots and Panthers, in which the referees decided to waive a possible pass interference call on Carolina's Luke Kuechly on the game's final play, costing the Patriots another chance at winning the game. While much of the conversation after the game focused on player positioning and the wording of the pass interference rule, what something more subliminal had contributed to the referees decision? Specifically, was the referees' decision was impacted by the game being played in Carolina? And, for instance, would officials have picked up the flag if that same play were to have occurred in New England?

Or how about Game 3 of the 2013 World Series, when St. Louis escaped with a win on an obstruction call against Boston's Will Middlebrooks. While the obstruction rule itself received most of the nation's attention in the days following the game, what if that identical game, situation, and play had happened at Fenway in the top of the 9th? Would Jim Joyce have had the gumption to call obstruction against the home team, and not in favor of it?

Of course, not every bad call goes against the visitors. One example of referees favoring the road team is Brett Hull's skate in the crease, and another is Michael Jordan's push off against the Jazz. However, Hull and Jordan were superstars, and superstar bias—the unintentional favoring of star players—is another possible, competing motivation for referee behavior. Also, in compiling the data from the controversial games lists, I took the liberty of not counting the 5th down game (Colorado at Missouri), because that game is controversial for referee incompetence, and not referee judgment.

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Here, I explain how referee home bias likely impacted both of those calls.

Scientific evidence supports a home bias

Beyond anecdotal examples, there are several noteworthy academic studies which shed light on how referee behavior is impacted by a home bias.

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In one paper, three UK researchers studied home field advantage in professional soccer, and found that home teams playing in stadia with running tracks (i.e., with a separation between fans and game action) received more penalties than home teams playing on pitches without running tracks. This suggests that referees were less likely to call infractions against the home team when pressure from within the stadium was higher. One obvious explanation is that without a running track, referees would be more likely to feel physically threatened by a boisterous crowd, which could be a reason to err on the side of the home team.

This makes sense—and the crazier the fan base, the more likely referees are to fear for their safety. Moreover, these fears are not unfounded; in recent years, soccer referees in both Brazil and Utah have been killed after violence resulting from controversial calls. Even in the English Premier League, where fan violence is less pronounced, but the fan bases are still more unruly than those in America, officials being swayed by the crowd has been suggested as one cause for the massive home field advantage in the league.

Beyond the threat of physical harm, there's also the possibility that referee decision making is impacted by crowd noise. This finding from a pair of German researchers identified that crowd noise itself acts as a cue, with context-specific cues helping indicate to referees what their appropriate reactions should be. Most often, these researchers suggest, such cues favor the home team. For example, when crowd noise starts to increase, such as at the end of a basketball game, referees may judge a play more harshly than if crowd noise was low (Hello, four-point play). Alternatively, in a sport such as figure skating, louder volume would potentially imply cheering, and thus be a cognitive signal of something positive happening, so judges might take those cues in a positive way.

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Off the field, these ideas have also been tested in a laboratory setting, by simply increasing and decreasing the volume in the room when soccer referees were forced to decide whether or not to give a yellow card. As it turned out in this experiment, a collaboration of four researchers from the US and the UK, volume of noise was indeed a primary influence in the cognitive process.

So we can just blame the referees?

Of course, we need to remember that referees are human. They get stressed by loud noises, by physical proximity (which implies the possibility of physical harm), and by the future thought of threat (which seems more imminent with a home crowd, in a home city). However, because all of these behaviors have been shown to affect human behavior in general, there is no good reason to expect that referees are any different. As a result, while you can certainly bitch and moan about how referee judgment in tight games favors the home team, what you might not realize is that referees are not the only ones who would make those decisions; unless you are a robot, you probably would too.

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If you are interested further studies of home bias, I recommend this study of stoppage time in soccer. Football Outsiders' Dannt Tuccitto has also written a paper on home field advantage in the NFL and its relationship with officiating. Further, Tobias Moskowitz and L. Jon Wertheim's Scorecasting book, which looks at borderline pitches in baseball and fumble recovery rates in football, is another great resource.